I've been changing my datapath to only have a single source/destination bus. I've run across one problem with the LOAD register. Normally, I will grab the data from the source and store it in the temporary holding register, then write the temp register to the destination on the next cycle.

When I do a LOAD, I take the source address and put it into the LOAD register. Which means I need to know both the source and destination at the same time. Or, the temp register doesn't have the valid data I need to put into the LOAD register.

1. The best idea I have come up with so far is to have ANOTHER temporary register which holds the source destination only for the purpose of putting it into the LOAD register. It's not a great solution.
2. I also thought about doing a look-ahead to see if the next instruction points to the LOAD register.
3. Or maybe a look behind to pull the previous byte from RAM into the LOAD register. After all, the data is in the RAM - I just need to get it out again. But that means more extra logic which means more chips.
4. Alternatively, I can ditch the LOAD functionality altogether. Instead just store 256 bytes in the ROM - one for each constant. So a LOAD would then be changing the data ram pointer to the constant area, then copying the correct constant out. And then change the data ram pointer back to where it was previously. It's a less elegant design, but it would be fewer chips. It might be problematic because what if I want to load a constant into the data ram pointer?
5. Maybe I could change how the LOAD register works. In other words, the LOAD register always contains the previous source location. So the LOAD register would only be valid for one instruction. That may be an acceptable solution. I'll have to check to make sure that logic works without adding more hardware.